Originally Posted by
mad_jock
I am not anti GPS.
And for certain situations ie above MSA the risk is low enough that its acceptable.
But below that there are so many external factors which effect the quality of of the position that the risk is unacceptable currently especially as there are no warnings when it does go out.
I suppose you could have a tone on a fequency which triggered when the local GPS strayed away outside tolerance from a fixed reference. Which would then flag in the cockpit.
bose the art of landing an aircraft when you can't feel anything from your knee down.
Assuming your GPS is approach approved you probably should get the owner/operator to have it checked out.
You should have RAIM integrity warnings that does give you your desired flag if the GPS position becomes unreliable. Also, it should be exceptionally rare for an approved installation to loose signal coverage - there must be something wrong with your installation or you are operating in known jamming areas.
Finally, GPS in and of itself is approved (even for Europe) at its basic level as the sole means of navigation to well below MSA. If you have WAAS then it is approved for approaches to ILS like minimums. (obviously it is always good to use the maximum amount of information to crosscheck any piece of magic - new or traditional)
In the US it is even approved for RNP approaches that no other navigation system provides the necessary accuracy and integrity to execute.